Machine tool probe with wireless signal transmission

Abstract

An optical signal transmission circuit for a probe is switched on by an optical switch-on signal comprising a burst 42 of pulses having a predetermined length. This is detected by a circuit which discriminates whether an input signal is a genuine switch-on signal or an interference burst 44 , on the basis of the duration of the switch-on signal.

What is claimed is:  
     
       1. A probe having a wireless signal transmission circuit, a detecting circuit for detecting an optical switch-on signal and switching on the signal transmission circuit when the switch-on signal is received, the detecting circuit including a time discriminating circuit which discriminates whether an input signal is a switch-on signal or interference on the basis of the duration of the switch-on signal. 
     
     
       2. A probe according to  claim 1 , wherein the time discriminating circuit determines that an input signal is a switch-on signal rather than the interference if its duration is longer than a first predetermined time period. 
     
     
       3. A probe according to  claim 2 , wherein the time discriminating circuit determines that the input signal is a switch-on signal rather than interference if its duration is also shorter than a second predetermined time period, the second predetermined time period being longer than the first. 
     
     
       4. A probe according to  claim 1 , wherein the time discriminating circuit determines that the input signal is a switch-on signal rather than interference if its duration is shorter than a predetermined time period. 
     
     
       5. A probe according to  claim 1 , wherein the time discriminating circuit includes a first circuit component with a fast time constant; and a second circuit component with a slow time constant; the second circuit component generating an output responsive to an average of an input signal while the first circuit component generates an output in response to shorter input signals; and a comparator connected to the outputs of the first and second components, to distinguish a switch-on signal from continuous interference. 
     
     
       6. A probe according to  claim 1  wherein, if the time discriminating circuit has determined that the duration of an input signal is consistent with a switch-on signal, it checks for the presence of an input signal after a further predetermined time period, thereby discriminating between a switch-on signal and recurring interference. 
     
     
       7. A probe according to  claim 1 , wherein the time discriminating circuit comprises a programmable device into which is programmed at least one time period which is predetermined in relation to the duration of the switch-on signal. 
     
     
       8. A method of switching on a probe having a wireless signal transmission circuit, the method comprising: 
       sending a wireless switch-on signal of a predetermined duration to the probe;  
       discriminating between the switch-on signal and interference on the basis of the duration of the switch-on signal; and  
       switching on the probe if the switch-on signal is detected.